method of defining a common frame of reference for a video game system

ABSTRACT

The invention relates to a method of defining a common frame of reference for a video game system. The system comprises at least two remotely-controlled vehicles ( 1 ), a first vehicle and a second vehicle, each comprising a video sensor ( 19 ), and a reference element ( 69 ) with recognizable zones ( 71 ). The method comprises the following steps: positioning the first vehicle relative to the reference element ( 69 ) in such a manner that the recognizable zones ( 71 ) are in the field of view of the video sensor ( 19 ) of the first vehicle; processing the image delivered by the video sensor ( 19 ) of the positioned first vehicle in order to identify the recognizable zones ( 71 ) in the image; deducing the position of the first vehicle relative to the reference element ( 69 ) by identifying the recognizable zones ( 71 ); and transmitting the position of the first vehicle to the second vehicle.

The invention relates to a method of defining a common frame ofreference for a video game system. In particular, the invention alsorelates to tracking objects in the common frame of reference.

Document WO 01/95988 A1 describes a hunting game for tworemotely-controlled vehicles. The vehicles are controlled by two users,and one of the two vehicles hunts the other. Each remotely-controlledvehicle is fitted with a video camera. The images delivered by the videocameras are communicated to two computers, with each of the twocomputers being used by one of the two players to control one of the tworemotely-controlled vehicles. Each player can thus see on the computerscreen the image delivered by the corresponding video camera of thatplayer's remotely-controlled vehicle.

In the above-mentioned hunting game application, the video image of thehunting vehicle is processed in such a manner that if the hunted vehiclecomes into the field of view of the video camera of the hunting vehicle,then the computer digitally removes the image corresponding to thehunted vehicle from the image delivered by the video camera of thehunting vehicle. The removed image of the hunted vehicle is replaced bya virtual character of the video game.

In this context, document WO 01/95988 envisages the hunted vehicle beingfitted with reflecting elements on essential points of its outsidesurface. These reflecting elements serve to make it easier to detect theimage of the hunted vehicle in the video image delivered by the videocamera of the hunting vehicle.

That document thus describes the use of recognizable zones, i.e.reflecting elements present on the hunted vehicle. However, such asystem does not enable both of the remotely-controlled vehicles to beput into a common frame of reference on initialization of the videogame.

Document U.S. Pat. No. 6,309,306A1also describes a system making itpossible in general manner to define a frame of reference common to tworemotely-controlled vehicles, but with the same limitations as in thepreviously described document.

The object of the present invention is thus to provide such a method ofdefining a common frame of reference.

According to the invention, this object is achieved by a method ofdefining a common frame of reference for a video game system, the systemcomprising:

-   -   at least two remotely-controlled vehicles, a first vehicle and a        second vehicle, each having a video sensor; and    -   a reference element with recognizable zones;

the method comprising the following steps:

-   -   positioning the first vehicle relative to the reference element        in such a manner that the recognizable zones are in the field of        view of the video sensor of the first vehicle;    -   processing the image delivered by the video sensor of the        positioned first vehicle in order to identify the recognizable        zones in the image;    -   deducing the position of the first vehicle relative to the        reference element by identifying the recognizable zones; and    -   transmitting the position of the first vehicle to the second        vehicle.

The common frame of reference of the invention is a single frame ofreference that is shared by the two remotely-controlled vehicles,enabling the respective positions of the two remotely-controlledvehicles to be initialized relative to a single origin point at thebeginning of the game and making it possible to track the movements ofthe two vehicles while the game is taking place.

The origin point of the common frame of reference is preferably definedby the reference element having the recognizable zones. In a preferredapplication, the reference element is a real object that is distinctfrom and independent of the two vehicles, in particular it is a bridgeor a pylon, serving to define a starting point for a race game betweentwo vehicles.

Alternatively, the reference element may also be incorporated in thesecond vehicle in the form of an arrangement of optical elements.

Under such circumstances, the reference element may be an arrangement oflights or reflecting elements of the kind to be found that the front andthe rear of motor vehicles.

Preferably, the recognizable zones of the reference element compriseoptical elements, in particular light-emitting diodes (LEDs) flashing atknown frequencies, or reflecting targets.

The two remotely-controlled vehicles are preferably toys in the form ofland vehicles, in particular racing cars or tanks, or aerial vehicles,in particular quadricopters.

In the steps of the method of the invention, the first vehicle isinitially placed close to the reference element. The location of thefirst vehicle needs to be selected in such a manner that therecognizable zones of the reference element come into the field of viewof the vehicle's video sensor. If the first vehicle is placed in such amanner that the image delivered by its video sensor does not reproducethe portion of the reference element that contains the recognizablezones, the image processing performed subsequently cannot detect therecognizable zones in the image delivered by the video camera. Undersuch circumstances, the first vehicle needs to be placed elsewhere inorder to enable the recognizable zones to be identified in the image.

Once the recognizable zones have been identified in the image, theposition of the first vehicle relative to the reference element isdeduced therefrom. This position may be expressed in the form of two- orthree-dimensional coordinates defining the position on the first vehiclerelative to the reference element that is used as the origin point inthe common frame of reference.

Finally, the position of the first vehicle as deduced is transmitted tothe second vehicle.

Preferably, the steps of image processing step and of deducing theposition of the first vehicle are performed by a computer on board thefirst vehicle.

Preferably, the image game system may also comprise at least twoelectronic entities, in particular two portable consoles, each servingto control a respective one of the two vehicles remotely. Under suchcircumstances, the video images delivered by the video sensors of theremotely-controlled vehicles can be displayed on the screens of theelectronic entities, and the steps of processing the images and deducingposition can be performed by computers present in the electronicentities.

Preferably, the position of the first vehicle relative to the referenceelement is deduced by triangulation.

In addition, communication between the remotely-controlled vehicles and,where appropriate, between the electronic entities and theremotely-controlled vehicles, such as transmitting the position of thefirst vehicle to the second vehicle, can be performed by short-rangeradio transmission, in particular using Bluetooth or WiFi protocol(registered trademarks).

The method of the invention possesses the major advantage of enabling asingle coordinate system to be established for a video game system thatincludes a plurality of remotely-controlled vehicles. Thus, wheninitializing a video game, such as a race game or a shooting game thatis to involve the two remotely-controlled vehicles, the system iscapable of knowing the exact positions of the vehicles involved in thegame, which is a prerequisite for reliably displaying and tracking thepositions of the vehicles during the video game. Such a method isparticularly advantageous for a video game system in which theremotely-controlled vehicles travel over arbitrary real terrain that isnot particularly prepared for video games, such as a park or a garden,and where the game takes place in a virtual game zone based on the realterrain.

When the various toys are in a common single frame of reference, one ormore virtual objects can be added to the game space.

For example, these may be virtual marks defining a car racing circuit,or virtual rings defining a circuit for flying quadricopters. The addedvirtual objects may move in the frame of reference. For example they maybe virtual cars traveling along the circuit or enemy airplanes movingaround the quadricopters. The objects are then displayed by beingencrusted in a 3D space of the game console used for controlling thetoy.

During the game period, the various vehicles, e.g. cars orquadricopters, preferably estimate their own movement and position. Thisis done by means of on-board sensors that may be accelerometers, gyros,video cameras, pressure sensors, and analog voltage sensors on drivemotors and steering motors. The measurements from the sensors may becombined and filtered by algorithms in a microcontroller on board theremotely-controlled vehicle. Thereafter, using radio means, each toy cantransmit its own position to all of the other toys, either each time itmoves, or at some given frequency, e.g. 25 times per second. In thisway, the coordinates of the moving vehicles are kept up to date,throughout the play of the game and in the common frame of referenceestablished during the initial sequence of the game.

By adding virtual objects in the three-dimensional space of the virtualgame and updating the positions of the toys in real time, the designerof the video game can stage complete interaction. The various video toyscan participate in the same game. The players can drive them. Gamescenarios may be cars racing around a virtual circuit, a game ofshooting one against another, or one with another and against virtualenemies, or flying in formation when piloting an airplane or aquadricopter.

There follows a description of implementations of methods of theinvention, and of devices and systems representing ways in which theinvention can be embodied, given with reference to the accompanyingdrawings in which the same numerical references are used from one figureto another to designate elements that are identical or functionallysimilar.

FIG. 1 is an overall view of the video game system of the invention;

FIGS. 2 a and 2 b show two examples of remote-controlled vehicles of theinvention;

FIGS. 3 a and 3 b are block diagrams of the electronic elements of aremotely-controlled vehicle of the invention;

FIGS. 4 a to 4 c show various examples of aerial images in the videogame system of the invention;

FIG. 5 shows a principle for defining game zones in the invention;

FIGS. 6 a and 6 b show the two-dimensional view of the invention;

FIGS. 7 a to 7 c show the perspective view of the invention;

FIG. 8 is an example of a view delivered by the video camera on boardthe remotely-controlled vehicle of the invention;

FIG. 9 shows an example of the display on the portable console of theinvention;

FIG. 10 shows the virtual positioning of a race circuit on an aerialimage of the invention;

FIG. 11 shows the method of adjusting the display of the invention;

FIGS. 12 a to 12 c show a method of defining a common frame of referenceof the invention; and

FIGS. 13 a to 13 c show an alternative version of a racing game of theinvention.

FIG. 1 gives an overall view of a system of the invention.

The system comprises a video game system constituted by aremotely-controlled vehicle 1 (referred to by the acronym BTT for“BlueTooth Toy”, or WIT, for “WiFiToy”) together with a portable console3 that communicates with the vehicle 1 via a Bluetooth link 5. Thevehicle 1 may be remotely-controlled by the portable console 3 via theBluetooth link 5.

The vehicle 1 is in communication with a plurality of satellites 7 via aGPS sensor on board the vehicle 1.

The portable console 3 may be fitted with a broadband wirelessconnection giving access to the Internet, such as a WiFi connection 9.

This connection enables the console 3 to access the Internet 11.

Alternatively, if the portable console is not itself fitted with anInternet connection, it is possible to envisage an indirect connectionto the Internet 13 via a computer 15.

A database 17 containing aerial images of the Earth is accessible viathe Internet 11.

By way of example, FIGS. 2 a and 2 b show two different embodiments ofthe remotely-controlled vehicle 1. In FIG. 2 a, the remotely-controlledvehicle 1 is a race car. This race car 1 has a video camera 19incorporated in its roof. The image delivered by the video camera 19 iscommunicated to the portable console 3 via the Bluetooth link 5 in orderto be displayed on the screen of the portable console 3.

FIG. 2 b shows that the remotely-controlled toy 1 may also beconstituted by a four-propeller “quadricopter” 21. As for the race car,the quadricopter 1 has a video camera 19 in the form of a dome locatedat the center thereof.

Naturally, the remotely-controlled vehicle 1 may also be in the form ofsome other vehicle, e.g. in the form of a boat, a motorcycle, or a tank.

To summarize, the remotely-controlled vehicle 1 is essentially a pilotedvehicle that transmits video, and that has sensors associated therewith.

FIGS. 3 a and 3 b are diagrams showing the main electronic components ofthe remotely-controlled vehicle 1.

FIG. 3 a shows in detail the basic electronic components. A computer 23is connected to various peripheral elements such as a video camera 19,motors 25 for moving the remotely-controlled vehicle, and variousmemories 27 and 29. The memory 29 is an SD card, i.e. a removable memorycard for storing digital data. The card 29 may be omitted, but it ispreferably retained since it serves to record the video image deliveredby the camera 19 so as to make it possible to look back through recordedvideo sequences.

FIG. 3 b shows the additional functions on board the remotely-controlledvehicle 1. The vehicle 1 essentially comprises two additional functions:an inertial unit 31 having three accelerometers 33 and three gyros 35,and a GPS sensor 37.

The additional functions are connected to the computer 23, e.g. via aserial link. It is also possible to add a USB (universal serial bus)connection to the vehicle 1 in order to be able to update the softwareexecuted in the electronic system of the vehicle 1.

The inertial unit 31 is an important element of the vehicle 1. It servesto estimate accurately and in real time the coordinates of the vehicle.In all, it estimates nine coordinates for the vehicle: the positions X,Y, and Z of the vehicle in three-dimensional space; the angles oforientation θ, ψ, φ of the vehicle (Eulerian angles); and the speeds VX,VY, and VZ along each of the three Cartesian axes X, Y, and Z.

These movement coordinates come from the three accelerometers 33 andfrom the three gyros 35. These coordinates may be obtained from a Kalmanfilter receiving the outputs from the measurements provided by thesensors.

More precisely, the microcontroller takes the measurement and forwardsit via the serial link or serial bus (serial peripheral interconnect,SPI) to the computer 23. The computer 23 mainly performs Kalmanfiltering and delivers the position of the vehicle 1 as determined inthis way to the game console 3 via the Bluetooth connection 5. Thefiltering calculation may be optimized: the computer 23 knows theinstructions that are delivered to the propulsion and steering motors25. It can use this information to establish the prediction of theKalman filter. The instantaneous position of the vehicle 1 as determinedwith the help of the inertial unit 31 is delivered to the game console 3at a frequency of 25 hertz (Hz), i.e. the console receives one positionper image.

If the computer 23 is overloaded in computation, the raw measurementsfrom the inertial unit 31 may be sent to the game console 3, which canitself perform the Kalman filtering instead of the computer 23. Thissolution is not desirable in terms of system simplicity and coherence,since it is better for all of the video game computation to be performedby the console and for all of the data acquisition to be performed bythe vehicle 1, but nevertheless it can be envisaged.

The sensors of the inertial unit 31 may be implemented in the form ofpiezoelectric sensors. These sensors vary considerably with temperature,which means that they need to be maintained at a constant temperaturewith a temperature probe and a rheostat, and that by using a temperatureprobe, it is necessary to measure the temperature level of thepiezoelectric sensors and to compensate in software for the variationsof the sensors with temperature.

The GPS sensor 37 is not an essential function of theremotely-controlled vehicle 1. Nevertheless, it provides great richnessin terms of functions at modest cost. A down-market GPS suffices,operating mainly outdoors and without any need for real time tracking ofthe path followed, since the real time tracking of the path is performedby the inertial unit 29. It is also possible to envisage using GPS inthe form of software.

The game console 3 is any portable console that is available on themarket. Presently-known examples of portable consoles are the Sonyportable Playstation (PSP) or the Nintendo Nintendo DS. It may beprovided with a Bluetooth key (dongle) 4 (cf. FIG. 1) for communicatingby radio with the vehicle 1.

The database 17 (FIG. 1) contains a library of aerial images, preferablyof the entire Earth. These photos may be obtained from satellites orairplanes or helicopters. FIGS. 4 a to 4 c show various examples ofaerial images that can be obtained from the database 17. The database 17is accessible via the Internet so that the console 3 can have accessthereto.

The aerial images downloaded from the database 17 are used by the gameconsole 3 to create synthesized views that are incorporated in the videogames that are played on the console 3.

There follows a description of the method whereby the console 3 acquiresaerial images from the database 17. For this purpose, the user of theconsole 3 places the remotely-controlled vehicle 1 at a real location,such as in a park or a garden, where the user seeks to play. By means ofthe GPS sensor 37, the vehicle 1 determines its terrestrial coordinates.These are then transmitted via the Bluetooth or WiFi link 5 to theconsole 3. The console 3 then connects via the WiFi link 9 and theInternet to the database 17. If there is no WiFi connection at the siteof play, the console 3 stores the determined terrestrial position.Thereafter the player goes to a computer 15 having access to theInternet. The player connects the console 3 to the computer and theconnection between the console 3 and the database 17 then takes placeindirectly via the computer 15. Once the connection between the console3 and the database 17 has been set up, the terrestrial coordinatesstored in the console 3 are used to search for aerial images or maps inthe database 17 that correspond to the terrestrial coordinates. Once animage has been found in the database 17 that reproduces the terrestrialzone in which the vehicle 1 is located, the console 3 downloads theaerial image that has been found.

FIG. 5 gives an example of the geometrical definition of atwo-dimensional games background used for a video game involving theconsole 3 and the vehicle 1.

The squares and rectangles shown in FIG. 5 represent aerial imagesdownloaded from the database 17. The overall square A is subdivided intonine intermediate rectangles. These nine intermediate rectangles includea central rectangle that is itself subdivided into 16 squares. Of these16 squares, the four squares at the center represent the game zone Bproper. This game zone B may be loaded at the maximum definition of theaerial images, and the immediate surroundings of the game zone B, i.e.the 12 remaining squares out of the 16 squares, may be loaded withaerial images at lower definition, and the margins of the game asrepresented by the eight rectangles that are not subdivided, and thatare located at the periphery of the subdivided central rectangle, may beloaded with aerial images from the database at even lower definition. Byacting on the definition of the various images close to or far away fromthe center of the game, the quantity of data that needs to be stored andprocessed by the console can be optimized while the visual effect andputting into perspective do not suffer. The images furthest from thecenter of the game are displayed with definition that corresponds totheir remoteness.

The downloaded aerial images are used by the console 3 to createdifferent views that can be used in corresponding video games. Moreprecisely, it is envisaged that the console 3 is capable of creating atleast two different views from the downloaded aerial images, namely avertical view in two dimensions (cf. FIGS. 6 a and 6 b) and aperspective view in three dimensions (cf. FIGS. 7 a to 7 c).

FIG. 6 a shows an aerial image as downloaded by the console 3. Theremotely-controlled vehicle 1 is located somewhere on the terrain viewedby the aerial image of FIG. 6 a. This aerial image is used to create asynthesized image as shown diagrammatically in FIG. 6 b. The rectangle39 represents the aerial image of FIG. 6 a. The rectangle 39 hasencrusted therein three graphics objects 41 and 43. These graphicsobjects represent respectively the position of the remotely-controlledvehicle on the game zone represented by the rectangle 39 (cf. spot 43that corresponds to the position of the remotely-controlled vehicle),and the positions of other real or virtual objects (cf. the crosses 41that may, for example, represent the positions of real competitors orvirtual enemies in a video game).

It is possible to envisage the software of the vehicle 1 taking care toensure that the vehicle does not leave the game zone as defined by therectangle 39.

FIGS. 7 a and 7 c show the perspective view that can be delivered by theconsole 3 on the basis of the downloaded aerial images. This perspectiveimage comprises a “ground” 45 with the downloaded aerial image insertedtherein. The sides 47 are virtual images in perspective at infinity,with an example thereof being shown in FIG. 7 b. These images aregenerated in real time by the three-dimensional graphics engine of thegame console 3.

As in the two-dimensional view, graphics objects 41 and 43 indicate tothe player the position of the player's own vehicle (43) and theposition of other players or potential enemies (41).

In order to create views, it is also possible to envisage downloading anelevation mesh from the database 17.

FIG. 8 shows the third view 49 that is envisaged in the video gamesystem, namely the view delivered by the video camera 19 on board theremotely-controlled vehicle 1. FIG. 8 shows an example of such a view.In this real video image, various virtual graphics objects are encrustedas a function the video game being played by the player.

FIG. 9 shows the game console 3 with a display that summarizes the wayin which the above-described views are presented to the player. Therecan clearly be seen the view 49 corresponding to the video imagedelivered by the video camera 19. The view 49 includes virtualencrustations 51 that, in FIG. 9, are virtual markers that define thesides of a virtual circuit. In the view 49, it is also possible to seethe real hood 53 of the remotely-guided vehicle 1.

The second view 55 corresponds to the two-dimensional vertical viewshown in FIGS. 6 a and 6 b. The view 55 is made up of the reproductionof an aerial image of the game terrain, having encrusted thereon avirtual race circuit 57 with a point 59 moving around the virtualcircuit 57. The point 59 indicates the actual position of theremotely-guided vehicle 1. As a function of the video game, thetwo-dimensional view 55 may be replaced by a perspective view of thekind described above. Finally, the display as shown in FIG. 9 includes athird zone 61, here representing a virtual fuel gauge for the vehicle 1.

There follows a description of an example of a video game for the videogame system shown in FIG. 1. The example is a car race performed on areal terrain with the help of the remotely-controlled vehicle 1 and thegame console 3, with the special feature of this game being that therace circuit is not physically marked out on the real terrain but ismerely positioned in virtual manner on the real game terrain on whichthe vehicle 1 travels.

In order to initialize the video race game, the user proceeds byacquiring the aerial image that corresponds to the game terrain in themanner described above. Once the game console 3 has downloaded theaerial image 39 reproducing a vertical view of the game terrain on whichthe vehicle 1 is located, the software draws a virtual race circuit 57on the downloaded aerial image 39, as shown in FIG. 10. The circuit 57is generated in such a manner that the virtual start line is positionedon the aerial image 39 close to the geographical position of the vehicle1. This geographical position of the vehicle 1 corresponds to thecoordinates delivered by the GPS module, having known physical valuesconcerning the dimensions of the vehicle 1 added thereto.

Using the keys 58 on the console 3, the player can cause the circuit 57to turn about the start line, can subject the circuit 57 to scalingwhile keeping the start line as the invariant point of the scaling (withscaling being performed in defined proportions that correspond to themaneuverability of the car), or can cause the circuit to slide aroundthe start line.

It is also possible to make provision for the start line to be movedalong the circuit, in which case the vehicle needs to move to the newstart line in order to start a game.

This can be of use, for example when the garden where the player seeksto play the video game is not large enough to contain the circuit asinitially drawn by the software. The player can thus change the positionof the virtual circuit until it is indeed positioned on the real gameterrain.

With a flying video toy that constitutes one of the preferredapplications, e.g. a quadricopter, an inertial unit of the flyingvehicle is used to stabilize it. A flight instruction is transmitted bythe game console to the flying vehicle, e.g. “hover”, “turn right”, or“land”. The software of the microcontroller on board the flying vehiclemakes use of its flight controls:

modifying the speed of the propellers or controlling aerodynamic flightsurfaces so as to make the measurements taken by the inertial unitcoincide with the flight instruction.

Likewise, with a video toy of the motor vehicle type, instructions arerelayed by the console to the microcontroller of the vehicle, e.g. “turnright” or “brake” or “speed 1 meter per second (m/s)”.

The video toy may have main sensors, e.g. a GPS and/or an inertial unitmade up of accelerometers or gyros. It may also have additional sensorssuch as video camera, means for counting the revolutions of the wheelsof a car, an air pressure sensor for estimating speed of a helicopter oran airplane, a water pressure sensor for determining depth in asubmarine, or analog-to-digital converters for measuring electricityconsumption at various points of the on-board electronics, e.g. theconsumption of each electric motor for propulsion or steering.

These measurements can be used for estimating the position of the videotoy on the circuit throughout the game sequence.

The measurement that is most used is that from the inertial unit thatcomprises accelerometers and/or gyros. This measurement can be checkedby using a filter, e.g. a Kalman filter, serving to reduce noise and tocombine measurements from other sensors, cameras, pressure sensors,motor electricity consumption measurements, etc.

For example, the estimated position of the vehicle 1 can be periodicallyrecalculated by using the video image delivered by the camera 19 and byestimating movement on the basis of significant fixed points in the theimage scene, which are preferably high contrast points in the videoimage. The distance to the fixed points may be estimated by minimizingmatrices using known triangulation techniques.

Position may also be recalculated over a longer distance (about 50meters) by using GPS, in particular recent GPS modules that measure thephases of the signals from the satellites.

The speed of the video toy may be estimated by counting wheelrevolutions, e.g. by using a coded wheel.

If the video toy is propelled by an electric motor, its speed can alsobe estimated by measuring the electricity consumption of said motor.This requires knowledge of the efficiency of the motor at differentspeeds, as can be measured beforehand on a test bench.

Another way of estimating speed is to use the video camera 19. For a caror a flying vehicle, the video camera 19 is stationary relative to thebody of the vehicle (or at least its position is known), and its focallength is also known. The microcontroller of the video toy performsvideo coding of MPEG4 type, e.g. using H263 or H264 coding. Such codinginvolves calculation predicting the movement of a subset of the imagebetween two video images. For example the subset may be a square of16*16 pixels. Movement prediction is preferably performed by a physicalaccelerometer. The set of movements of the image subset provides anexcellent measurement of the speed of the vehicle. When the vehicle isstationary, the sum of the movements of the subsets of the image isclose to zero. When the vehicle is advancing in a straight line, thesubsets of the image move away from the vanishing point with a speedthat is proportional to the speed of the vehicle.

In the context of the race car video game, the screen is subdivided intoa plurality of elements, as shown in FIG. 9. The left element 49displays the image delivered by the video camera 19 of the car 1. Theright element 55 shows the map of the race circuit together withcompeting cars (cf. the top right view in FIG. 9).

Indicators may display real speed (at the scale of the car). Gameparameters may be added, such as the speed or the fuel consumption ofthe car, or they may be simulated (as for a Formula 1 grand prix race).

In the context of this video game, the console can also store races. Ifonly one car is available, it is possible to race against oneself. Undersuch circumstances, it is possible to envisage displaying transparentlyon the screen a three-dimensional image showing the position of the carduring a stored lap.

FIG. 11 shows in detail how virtual encrustations 51, i.e. race circuitmarkers, are adapted in the display 49 corresponding to the view fromthe corresponding video camera on board the vehicle 1. FIG. 11 is asideview showing the topography 63 of the real terrain on which the vehicle1 is moving while playing the race video game. It can be seen that theground of the game terrain is not flat, but presents ups and downs. Theslope of the terrain varies, as represented by arrows 65.

Consequently, the encrustation of the circuit markers 51 in the videoimage cannot be static but needs to adapt as a function of the slope ofthe game terrain. To take this problem into account, the inertial unit31 of the vehicle 1 has a sensor for sensing the attitude of thevehicle. The inertial sensor performs real time acquisition of theinstantaneous attitude of the vehicle 1. From instantaneous attitudevalues, the electronics of the vehicle 1 estimate two values, namely theslope of the terrain (i.e. the long-term average of the attitude) andthe roughness of the circuit (i.e. the short-term average of theattitude). The software uses the slope value to compensate the display,i.e. to move the encrusted markers 51 on the video image, as representedby arrow 67 in FIG. 11.

Provision is also made to train the software that adjusts the display ofthe markers 51. After the vehicle 1 has traveled a first lap round thevirtual circuit 57, the values for slope and roughness all around thecircuit are known, stored, and used in the prediction component of aKalman filter that re-estimates slope and roughness on the next lap.

The encrustation of the virtual markers 51 on the video image can thusbe improved by displaying only discontinuous markers and by displaying asmall number of markers, e.g. only four markers on either side of theroad. Furthermore, the distant markers may be of a different color andmay serve merely as indications and not as real definitions of theoutline of the track. In addition, the distant markers may also beplaced further apart than the near markers.

Depending on the intended application, it may also be necessary toestimate the roll movement of the car in order to adjust the positionsof the markers 51, i.e. to estimate any possible tilt of the car aboutits longitudinal axis.

The circuit roughness estimate is preferably used to extract the slopemeasurement from the data coming from the sensor.

In order to define accurately the shape of the ground on which thecircuit is laid, a training stage may be performed by the video game.This training stage is advantageously performed before the game proper,at a slow and constant speed that is under the control of the gameconsole. The player is asked to take a first lap around the circuitduring which the measurements from the sensors are stored. At the end ofthe lap round the track, the elevation values of numerous points of thecircuit are extracted from the stored data. These elevation values aresubsequently used during the game to position the virtual markers 51properly on the video image.

FIGS. 12 a to 12 c show a method of defining a common frame of referencewhen the race game is performed by two or more remotely-controlledvehicles 1. In this context, there are two players each having aremotely-controlled vehicle 1 and a portable console 3. These twoplayers seek to race two cars against each other around the virtual racecircuit 57 using their two vehicles 1. The initialization of such atwo-player game may be performed, for example, by selecting a “two-car”mode on the consoles. This has the effect of the Bluetooth or WiFiprotocol in each car 1 entering a “partner search” mode. Once thepartner car has been found, each car 1 informs its own console 3 thatthe partner has been found. One of the consoles 1 is used for selectingthe parameters of the game: selecting the race circuit in the mannerdescribed above, the number of laps for the race, etc. Then a countdownis started on both consoles: the two cars communicate with each otherusing the Bluetooth or WiFi protocol. In order to simplify exchangesbetween the various peripherals, each car 1 communicates with its ownconsole 3 but not with the consoles of the other cars. The cars 1 thensend their coordinates in real time and each car 1 sends its owncoordinates and the coordinates of the competitor(s) to the console 3from which it is being driven. On the console, the display of thecircuit 55 shows the positions of the cars 1.

In such a car game, the Bluetooth protocol is in a “Scatternet” mode.One of the cars is then a “Master” and the console with which it ispaired is a “Slave”, and the other car is also a “Slave”. In addition,the cars exchange their positions with each other. Such a race game withtwo or more remotely-controlled vehicles 1 requires the cars 1 toestablish a common frame of reference during initialization of the game.FIGS. 12 a to 12 c show details of defining a corresponding common frameof reference.

As shown in FIG. 12 a, the remotely-controlled vehicles 1 with theirvideo cameras 19 are positioned facing a bridge 69 placed on the realgame terrain. This real bridge 69 represents the starting line and ithas four light-emitting diodes (LEDs) 71. Each player places thecorresponding car 1 in such a manner that at least two of the LEDs 71are visible on the screen of the player's console 3.

The LEDs 71 are of known colors and they may flash at known frequencies.In this way, the LEDs 71 can easily be identified in the video imagesdelivered respectively by the two video cameras 19. A computer presenton each of the vehicles 1 or in each of the consoles 3 processes theimage and uses triangulation to estimate the position of thecorresponding car 1 relative to the bridge 69.

Once a car 1 has estimated its position relative to the bridge 69, ittransmits its position to the other car 1. When both cars 1 haveestimated their respective positions relative to the bridge 69, thepositions of the cars 1 relative to each other are deduced therefrom andthe race can begin.

FIG. 12 b is a view of the front of the bridge 69 showing the four LEDs71. FIG. 12 c shows the display on the console 3 during the procedure ofdetermining the position of a vehicle 1 relative to the bridge 69. InFIG. 12 c, it can clearly be seen that the computer performing imageprocessing has managed to detect the two flashing LEDs 71, as indicatedin FIG. 12 c by two cross-hairs 73.

Defining a common frame of reference relative to the ground and betweenthe vehicles is particularly useful for a race game (each vehicle needsto be referenced relative to the race circuit).

For some other video games, such as a shooting game, defining a commonframe of reference is simpler: for each vehicle, it suffices to know itsposition relative to its competitors.

FIGS. 13 a to 13 c are photos corresponding to an alternative version ofthe race video game, the race game now involving not one or more cars 1,but rather one or more quadricopters 1 of the kind shown in FIG. 2 b.Under such circumstances, where the remotely-controlled vehicle 1 is aquadricopter, the inertial unit is not only used for transmitting thethree-dimensional coordinates of the toy to the console 3, but also forproviding the processor on board the quadricopter 1 with the informationneeded by the program that stabilizes the quadricopter 1.

With a quadricopter, the race no longer takes place on a track as itdoes for a car, but is in three dimensions. Under such circumstances,the race follows a circuit that is no longer represented by encrustedvirtual markers as shown in FIG. 9, but that is defined for example byvirtual circles 75 that are encrusted in the video image (cf. FIG. 13 b)as delivered by the video camera 19, said circle floating in threedimensions. The player needs to fly the quadricopter 1 through thevirtual circles 75.

As for the car, three views are possible: the video image delivered bythe video camera 19 together with its virtual encrustations, thevertical view relying on a downloaded aerial image, and the perceptiveview likewise based on a downloaded satellite or aerial image.

FIG. 13 b gives an idea of a video image of encrusted virtual circles 75of the kind that may arise during a game involving a quadricopter.

The positioning of the race circuit on the downloaded aerial image isdetermined in the same manner as for a car race. The circuit ispositioned by hand by the player in such a manner as to be positionedsuitably as a function of obstacles and buildings. Similarly, the usercan scale the circuit, can turn it about the starting point, and cancause the starting point to slide around the track. The step ofpositioning the circuit 57 is shown in FIG. 13 a.

In the same manner as for a car race, in a race involving a plurality ofquadricopters, provision is made for a separate element to define thestarting line, e.g. a pylon 77 carrying three flashing LEDs or reflectorelements 71. The quadricopters or drones are aligned in a common frameof reference by means of the images from their cameras 19 and thesignificant points in the images as represented by the three flashingLEDs 71 of the pylon 77. Because all these geometrical parameters areknown (camera position, focal length, etc.), the vehicle 1 is positionedwithout ambiguity in a common frame of reference. More precisely, thevehicle 1 is positioned in such a manner as to be resting on the groundwith the pylon 77 in sight, and then it is verified on the screen of itsconsole 3 that all three flashing LEDs 71 can be seen. The threeflashing LEDs 71 represent significant points in recognizing the frameof reference. Because they are flashing at known frequencies, they caneasily be identified by the software.

Once the position relative to the pylon 77 is known, the quadricopters 1exchange information (each conveying to the other its position relativeto the pylon 77) and in this way each quadricopter 1 deduces theposition of its competitor.

The race can begin from the position of the quadricopter 1 from whichthe pylon 77 was detected by image processing. Nevertheless, it isnaturally also possible to start the race from some other position, theinertial unit being capable of storing the movements of thequadricopters 1 from their initial position relative to the pylon 77before the race begins.

Another possible game is a shooting game between two or more vehicles.For example, a shooting game may involve tanks each provided with afixed video camera or with a video camera installed on a turret, orindeed it may involve quadricopters or it may involve quadricoptersagainst tanks. Under such circumstances, there is no need to know theposition of each vehicle relative to a circuit, but only to know theposition of each vehicle relative to the other vehicle(s). A simplerprocedure can be implemented. Each vehicle has LEDs flashing at a knownfrequency, with known colors, and/or in a geometrical configuration thatis known in advance. By using the communications protocol, each vehicleexchanges with the others information concerning its type, the positionsof its LEDs, the frequencies at which they are flashing, their colors,etc. Each vehicle is placed in such a manner that at the beginning ofthe game, the LEDs of the other vehicle are in the field of view of itsvideo sensor 19. By performing a triangulation operation, it is possibleto determine the position of each vehicle relative to the other(s).

The game can then begin. Each vehicle, by virtue of its inertial unitand its other measurement means, knows its own position and itsmovement. It transmits this information to the other vehicles.

On the video console, the image of an aiming site is encrusted, e.g. inthe center of the video image transmitted by each vehicle. The playercan then order projectiles to be shot at another vehicle.

At the time a shot is fired, given the position forwarded by the othervehicles and its own position direction and speed, the software of theshooting vehicle can estimate whether or not the shot will reach itstarget. The shot may simulate a projectile that reaches it targetimmediately, or else it may simulate the parabolic flight of a munition,or the path of a guided missile. The initial speed of the vehicle firingthe shot, the speed of the projectile, the simulation of externalparameters, e.g. atmospheric conditions, can all be simulated. In thisway, shooting in the video game can be made more or less complex. Thetrajectory of missile munitions, tracer bullets, etc., can be displayedby being superimposed on the console.

The vehicles such as land vehicles or flying vehicles can estimate thepositions of other vehicles in the game. This can be done by a shaperecognition algorithm making use of the image from the camera 19.Otherwise, the vehicles may be provided with portions that enable themto be identified, e.g. LEDs. These portions enable other vehiclescontinuously to estimate their positions in addition to the informationfrom their inertial units as transmitted by the radio means. Thisenables the game to be made more realistic. For example, during a battlegame against one another, one of the players may hide behind a featureof the terrain, e.g. behind a tree. Even though the video game knows theposition of the adversary because of the radio means, that position willnot be shown on the video image and the shot will be invalid even if itwas in the right direction.

When a vehicle is informed by its console that it has been hit, or ofsome other action in the game, e.g. simulating running out of fuel, abreakdown, or bad weather, a simulation sequence specific to the videogame scenario may be undertaken. For example, with a quadricopter, itmay start to shake, no longer fly in a straight line, or make anemergency landing. With a tank, it may simulate damage, run more slowly,or simulate the fact that its turret is jammed. Video transmission mayalso be modified, for example the images may be blurred, dark, oreffects may be encrusted on the video image, such as broken cockpitglass.

The video game of the invention may combine:

-   -   player actions: driving the vehicles;    -   virtual elements: a race circuit or enemies displayed on the        game console; and    -   simulations: instructions sent to the video toy to cause it to        modify its behavior, e.g. an engine breakdown or a speed        restriction on the vehicle, or greater difficulty in driving it.

These three levels of interaction make it possible to increase therealism between the video game on the console and a toy provided withsensors and a video camera.

1. A method of defining a common frame of reference for a video game system (1, 3), the system comprising: at least two remotely-controlled vehicles (1), a first vehicle and a second vehicle, each having a video sensor (19); and a reference element (69) with recognizable zones (71); the method being characterized in that it comprises the following steps: positioning the first vehicle relative to the reference element (69) in such a manner that the recognizable zones (71) are in the field of view of the video sensor (19) of the first vehicle; processing the image delivered by the video sensor (19) of the positioned first vehicle in order to identify the recognizable zones (71) in the image; deducing the position of the first vehicle relative to the reference element (69) by identifying the recognizable zones (71); and transmitting the position of the first vehicle to the second vehicle.
 2. A method according to claim 1, the reference element (69) being a real object that is distinct from and independent of the two vehicles, in particular a bridge or a pylon, and serving to define a starting point for a race game between the two vehicles.
 3. A method according to claim 1, the reference element (69) being incorporated in the second vehicle in the form of an arrangement of optical elements.
 4. A method according to claim 1, wherein the recognizable zones (71) comprise optical elements, in particular LEDs flashing at known frequencies, or reflective targets.
 5. A method according to claim 1, wherein the position of the first vehicle relative to the reference element (69) is deduced by triangulation.
 6. A method according to claim 1, wherein the video game system (1, 3) further comprises at least two electronic entities (3), in particular two portable consoles, each serving to control a respective one of the two vehicles (1) remotely.
 7. A method according to claim 1, the two remotely-controlled vehicles being land vehicles, in particular racing cars or tanks, or aerial vehicles, in particular quadricopters.
 8. A method according to claim 6, communication between the electronic entities (3) and the remotely-controlled vehicles (1), and communication between the vehicles themselves, being performed by short-range radio transmission (5), in particular using Bluetooth or WiFi protocol.
 9. A method according to claim 1, wherein the remotely-controlled vehicles (1) have means for estimating their movements and/or their positions.
 10. A method according to claim 9, wherein the movement and/or position estimating means comprise the video sensor (19).
 11. A method according to claim 9, wherein the movement and/or position estimation means comprise an inertial unit made up of one or more accelerometers and/or one or more gyros.
 12. A method according to claim 9, wherein the movement and/or position estimation means comprise analog-to-digital electronic converters measuring the electricity consumption of electric motors of the remotely-controlled vehicles (1) in order to estimate their speeds.
 13. A method according to claim 9, wherein the movement and/or position estimation means comprise pressure sensors, in particular Pitot tubes.
 14. A method according to claim 9, wherein the movement and/or position estimation means comprise a GPS sensor.
 15. A method according to claims 9, wherein each remotely-controlled vehicle (1) has a computer provided with data filtering and merging algorithms so as to enable the most likely magnitudes to be estimated from the data coming from all of the sensors.
 16. A method according to claim 18, wherein radio transmission takes place in real time to enable all of the other remotely-controlled vehicles (1) to estimate their movements and/or positions.
 17. A method according to claim 16, wherein the radio transmission comprises updating movement and/or position estimates at the same frequency as video image encoding, in particular 25 times per second.
 18. A method according to claim 8, wherein the remotely-controlled vehicles (1) have means for estimating their movements and/or their positions.
 19. A method according to claim 10, wherein the movement and/or position estimation means comprise an inertial unit made up of one or more accelerometers and/or one or more gyros.
 20. A method according to claim 10, wherein the movement and/or position estimation means comprise analog-to-digital electronic converters measuring the electricity consumption of electric motors of the remotely-controlled vehicles (1) in order to estimate their speeds.
 21. A method according to claim 11, wherein the movement and/or position estimation means comprise analog-to-digital electronic converters measuring the electricity consumption of electric motors of the remotely-controlled vehicles (1) in order to estimate their speeds. 